A glass window or other glass article is said to have the desirable color “grey” when it has a dominant wavelength of from 435 nm to 570 nm (this dominant wavelength range defines the color “grey” herein).
While glass having “grey” color is often desirable, as explained above there sometimes also exists a need or desire to achieve certain levels of x and y color values, and sometimes of light transmission defined conventionally by:                Lta as visible light transmission,        UV as ultraviolet light transmission, and        IR as infrared light transmission.        
Glass thickness ranges of from about 1-6 mm, more preferably from about 3-4 mm, are typically used when measuring the aforesaid characteristics. These thickness ranges are generally recognized as conventional thicknesses for glass sheets made by the float glass process.
Certain grey glasses achieve their desired grey coloration by using a combination of selenium (Se) and chromium (Cr) oxide colorants. For example, see U.S. Pat. Nos. 5,877,103 and 5,728,471. However, the use of significant amounts of Se and/or Cr is not always desirable. For purposes of example only and without limiting any claim in any way, raw materials used to intentionally introduce chromium into glass batches can sometimes be difficult to melt and may lead to chromite defects in certain situations. Moreover, for purposes of example only and without limiting any claim in any way, the amount of Se that is retained in a glass from the batch to the final glass product (i.e., Se retention) may vary from day to day, or week to week, depending on processing parameters thereby leading to possible color variations.
In view of the above, while trace amounts of chromium and/or Se may end up in a final glass product, there exists a need in the art to make a soda-lime-silica based glass which can achieve desired grey color while primarily relying on colorants other than Se and/or Cr. While trace amounts of Se and/or Cr may end up in the glass, there is a need to create a glass which can achieved desired grey coloration while minimizing the amounts of one or both of these materials.
Other have tried to make grey glass without using significant amounts of Se and/or Cr. For example, a known glass believed to be sold by St. Gobain has a colorant portion of 0.364% total iron, 199 ppm Co3O4, 8 ppm Cr2O3, and 780 ppm NiO. Likewise, another known glass believed to be sold by Asahi has a colorant portion of 0.198% total iron, 189 ppm Co3O4, 11 ppm Cr2O3, and 829 ppm NiO. The St. Gobain glass achieves a visible transmission of about 16% (at 0.219 inches thickness), desired grey x and y color values of 0.2929 and 0.3121, a dominant wavelength of 488, an excitation purity of 6.75 and a % FeO of 0.1053. The Asahi glass achieves a visible transmission of about 16% (at 0.219 inches thickness), desired grey x and y color values of 0.2932 and 0.3084, a dominant wavelength of 485, an excitation purity of 6.99 and a % FeO of 0.0857. While these glasses achieved desired grey coloration, they are typically difficult to fine-tune with respect to coloration. In a manner, see U.S. Pat. No. 6,764,973, which is similarly flawed.
It is noted that the instant inventors have used erbium oxide in grey glasses. For example, see U.S. Pat. Nos. 6,521,558 and 6,573,207, which are hereby incorporated herein by reference. However, the erbium oxide used in these patents (i.e., '558 and '207 patents) is used in combination with substantial amounts of Se in order to achieve desired coloration. As explained above, the use of significant amounts of Se is not always desirable.
In view of the above, it will be apparent that there exists a need in the art for a soda-lime-silica based glass which can achieve desired grey color while primarily relying on colorants other than Se and/or Cr, and which uses colorants which permit color to be more easily fine-tuned.